For all the danger posed to Florida's Everglades by invasive Burmese pythons, there's one thing researchers don't want to know: how they would interact with another python species that threatens to move into the same territory.

The number of Monarch butterflies that reached wintering grounds in Mexico has rebounded 69 percent from last year's lowest-on-record levels, but their numbers remain very low, according to the World Wildlife Fund.

La Nina, a weather phenomenon that periodically causes devastating droughts and storms, will likely occur more frequently and more violently this century as a result of global warming, researchers said Monday.